The present invention relates to an oil pressure controlling apparatus for continuously variable transmission (CVT).
As illustrate in FIGS. 1A and 1B, a CVT 500 is mainly provided with a primary shaft 520 and a secondary shaft 530 arranged in parallel, a primary pulley 550 and a secondary pulley 570 attached to the shafts 520 and 530, respectively, and a drive belt 590 passed over the pulleys 550 and 570.
The CVT 500 continuously varies the speed ratio of driving and driven elements over working range by varying an effective winding ratio of the drive belt 590 to the pulleys 550 and 570.
The primary pulley 550 has a fixed pulley 550a that is driven via a torque converter and a forward/backward-switching mechanism, etc., and a slidable pulley 550b. The slidable pulley 550b is attached to the shaft of the fixed pulley 550a via ball splines 550c for varying a pulley-groove width so that the slidable pulley 550b is slidable in the direction of the shaft and rotates with the fixed pulley in a uniform motion with respect to each other. A transmission oil-pressure cylinder 560 consists of a cylinder 560a fixed at the back of the slidable pulley 550b and a plunger 560b attached to the shaft of the fixed pulley 550a. 
Likewise, the secondary pulley 570 has a fixed pulley 570a connected to drive wheels via a reduction mechanism, etc. A slidable pulley 570b is attached to the shaft of the fixed pulley 570a via ball splines 570c so that the slidable pulley 570b is slidable in the direction of the shaft and rotates with the fixed pulley in a uniform motion with respect to each other. A transmission oil-pressure cylinder 580 consists of a cylinder 580a fixed to the back of the slidable pulley 570b and a plunger 580b attached to the shaft of the fixed pulley 570a. 
Oil pressure applied by an oil pump to the oil pressure cylinders 560 and 580 provided at the primary pulley 550 and the secondary pulley 570, respectively, are controlled for power transfer and transmission control between the drive belt 590 and the primary and the secondary pulleys 550 and 570.
The primary and the secondary pulleys 550 and 570 are rotating at a predetermined rotational ratio while the CVT 500 is operating. The rotation of pulleys causes generation of centrifugal oil pressure to the oil pressure cylinders 560 and 580.
The centrifugal oil pressure generated to the oil pressure cylinder 560 provided in the primary pulley 550 is applied thereto in a up-shift direction to force the pulley-groove width to be narrow, or to overdrive (OD) in transmission.
Contrary to this, the centrifugal oil pressure generated to the oil pressure cylinder 580 provided in the secondary pulley 570 is applied thereto in a shift-down direction to force the pulley-groove width to be narrow, or to LOW in transmission.
A balance oil chamber 610 is formed on the back of the plunger 560b as a part of the oil pressure cylinder 560 for the primary pulley 550. The balance oil chamber 610 is filled with oil to generate centrifugal oil pressure that cancels force applied in the OD direction due to generation of centrifugal oil pressure in the oil pressure cylinder 560.
Moreover, a balance oil chamber 620 is formed on the back of the plunger 580b by means of a balance oil chamber cylinder 580d, one end of which is connected to a tip of a cylinder portion 580a that is a part of the oil pressure cylinder 580 and the other end is set as slidable along the shaft of a fixed pulley 570a. The balance oil chamber 620 is filled with oil to generate centrifugal oil pressure that cancels force applied in the LOW direction due to generation of centrifugal oil pressure in the oil pressure cylinder 580.
A lubricant is always supplied by an oil pump (not shown) into the balance oil chamber 620 formed in the secondary pulley 570. Shift-down from OD to LOW in transmission speed of the CVT 500 displaces the slidable pulley 570b to left in FIG. 1B (in the direction of the fixed pulley 750a) due to oil pressure applied to the oil cylinder 580 of the secondary pulley 570. This results in contraction of the volume of the balance oil chamber 620 so that the lubricant in the chamber 620 is extruded through a gap 630 formed between the shaft of the fixed pulley 570a and the end of the balance oil cylinder 58d. 
Oil pressure used for control and lubrication in the CVT 500 is obtained by the oil pump driven by an engine (not shown). Change in transmission speed by varying the groove-width of the primary and the secondary pulleys 550 and 570 requires enough oil in the oil pump to follow change in volume of the oil cylinders 560 and 580 for prevention of a slip of the drive belt 590 which would otherwise happen due to decrease in clamping power of the belt 590. The oil amount in the oil pump is set for attaining oil flow required for lubrication to forward/backward-switching, etc.
As discussed, energy for driving the oil pump is increased for supplying enough oil to cover energy loss caused by sliding resistance generated in each component. Such energy for the oil pump is also increased to supply oil to components at a pulley-transmission control pressure even though the components operate at a pressure lower than the pulley-transmission control pressure.
The CVT 500 smoothly performs transmission speed control by restricting unnecessary force which would otherwise be generated due to generation of centrifugal oil pressure in the oil pressure cylinders 560 and 580, with the structure in that the balance oil chamber 610 is formed on the back of the plunger 560b as a part of the oil pressure cylinder 560 of the primary pulley 550 and the balance oil chamber 620 is formed on the back of the plunger 580b as a part of the balance oil chamber cylinder 580d of the secondary pulley 570.
The balance oil chamber 620 formed in the secondary pulley 570 is, however, always filled with the lubricant supplied by the oil pump, which causes increase in amount of the lubricant required for CVT operation, thus the oil pump becoming bulk to increase mechanical loss and fuel consumption.
A purpose of the present invention is to provide an oil pressure control apparatus for CVTs, that decreases consumption of a lubricant supplied by a oil pump.
Another purpose of the present invention is to provide an oil pressure control apparatus for CVTs, that decreases consumption of a lubricant for compactness of an oil pump with decrease in mechanical loss and fuel consumption.
The present invention provides an oil-pressure control apparatus for a continuously variable transmission having a primary pulley and a secondary pulley, a belt being passed around the primary and the secondary pulleys, the apparatus including: a primary cylinder provided for the primary pulley, having an oil chamber for applying an oil pressure to the primary pulley and a balance oil chamber for applying a centrifugal oil pressure to the primary pulley in a direction which is reverse of a centrifugal oil pressure generated in the oil chamber; a primary valve for adjusting a primary pressure to be applied to the oil chamber based on a line pressure applied by an oil pump; and a balance oil line that connects a drain port of the primary valve and the balance oil chamber, oil being supplied from the primary valve to the balance oil chamber through the balance oil line.
Moreover, the present invention provides an oil-pressure control apparatus for a continuously variable transmission having a primary pulley and a secondary pulley, a belt being passed around the primary and the secondary pulleys, the apparatus including: a primary cylinder provided for the primary pulley, having a primary chamber for applying an oil pressure to the primary pulley and a primary balance oil chamber for applying a centrifugal oil pressure to the primary pulley in a direction which is reverse of a centrifugal oil pressure generated in the primary chamber; a secondary cylinder provided for the secondary pulley, having a secondary chamber for applying an oil pressure to the secondary pulley and a secondary balance oil chamber for applying a centrifugal oil pressure to the secondary pulley in a direction which is reverse of a centrifugal oil pressure generated in the secondary oil chamber; a balance oil line that connects a cooling line and the balance oil chamber, an oil cooler being provided in midstream of the cooling line, oil passing through the oil cooler being supplied to the primary and the secondary balance chambers through the balance oil line.
Furthermore, the present invention provides an oil-pressure control apparatus for a continuously variable transmission having a primary pulley and a secondary pulley, a belt being passed around the primary and the secondary pulleys, the apparatus including: a fixed pulley fixed at a secondary shaft of the secondary pulley; a slidable pulley attached to a shaft of the fixed pulley, the slidable pulley being slidable in a direction of the shaft of the fixed pulley and rotating with the fixed pulley in a uniform motion with respect to each other; a transmission oil-pressure cylinder having a cylinder fixed at the back of the slidable pulley and a plunger fixed at the shaft of the fixed pulley; a balance oil chamber formed by the cylinder, the plunger and a balance oil chamber cylinder, one end of the balance oil chamber cylinder being connected to the cylinder, the other end of the balance oil chamber cylinder being slidably connected to the shaft of the fixed pulley via a gap, the balance oil chamber canceling a centrifugal oil pressure generated due to rotation of the pulleys; and a balance oil-pressure control valve for supplying a lubricant to the balance oil chamber, the balance oil-pressure control valve being closed while the lubricant supplied to the balance oil chamber is being drained therefrom.
Moreover, the present invention provides an oil-pressure control apparatus for a continuously variable transmission having a primary pulley and a secondary pulley, a belt being passed around the primary and the secondary pulleys, the apparatus including: a fixed pulley fixed at a secondary shaft of the secondary pulley; a slidable pulley attached to a shaft of the fixed pulley, the slidable pulley being slidable in a direction of the shaft of the fixed pulley and rotating with the fixed pulley in a uniform motion with respect to each other; a transmission oil-pressure cylinder having a cylinder fixed at the back of the slidable pulley and a plunger fixed at the shaft of the fixed pulley; a balance oil chamber formed by the cylinder, the plunger and a balance oil chamber cylinder, one end of the balance oil chamber cylinder being connected to the cylinder, the other end of the balance oil chamber cylinder being slidably connected to the shaft of the fixed pulley via a seal, the balance oil chamber canceling a centrifugal oil pressure generated due to rotation of the pulleys; and a balance oil-pressure control valve for supplying a lubricant to the balance oil chamber through a lubricant-pressure line, the lubricant being drained from the lubricant-pressure line and the balance oil-pressure control valve being closed to stop supply of the lubricant to the balance oil chamber when an oil pressure on the lubricant-pressure line is a predetermined pressure or higher.